The data provided here are corrected absolute gravity data and free-air anomalies. The absolute gravity
data are a combination of relative gravity data measured by the shipboard gravity meter and the absolute gravity data of the ports in
departure and arrival. Drift corrections and the Eoetvoes corrections were done before converting into absolute gravity. As a quality
control, low reliability data were removed (see section 6. for the judging criteria). The absolute gravity values of the ports are
referenced to those of the Japan Gravity Standardization Net of the Geographical Survey Institute of Japan.

Measurement System

(1) Shipboard gravity meter The system consists of two main assemblies; the gyro-stabilized platform including the gravity sensor and
the data handling & control system.

(2) Portable gravity meter The portable gravity meter consists of two modules; the data acquisition/control
module and the gravity sensor module. The gravity sensor is enclosed in a thermostatically controlled vacuum chamber. The portable gravity
meter is used to calculate the absolute gravity of the port with reference to the gravity station of the Japan Gravity Standardization Net
of the Geographical Survey Institute of Japan.

According to the filter process of the gravity meter system, the gravity data has a time lag of 180 seconds between the measurement and its
output. After adjustment of this lag time, the following corrections and calculations were performed.

(1) Drift correction

D = ((Vge-Vgs)-(Age-Ags))/(Te-Ts)

D: Drift value (mGal/day) Vgs: The shipboard gravity at the start of the cruise (mGal) Vge: The shipboard gravity at the
end of the cruise (mGal) Ags: The absolute gravity at the shipboard sensor position at the start of the cruise (mGal) Age:
The absolute gravity at the shipboard sensor position at the end of the cruise (mGal) Ts: The start time of the cruise (day)
Te: The end time of the cruise (day)

* The navigation data such as S,φand αare the 4-min average values. Before average processing, following data were removed from
each dataset. If the number of data used for a 4-min average calculation did not include more than 50% of good data, the processed average
value was considered as a missing value. ⋅ Time error (inversion of time, continuation of same timestamps) ⋅ Ship
speed exceeding 20knot ⋅ Course of the ship except 0-360°

(3) Calculation of the absolute gravity

G = Ags+(Vg-Vgs)-D*(T-Ts)+E+H*β

G: The absolute gravity at sea surface (mGal) Ags: The absolute gravity at the shipboard sensor position at the start of the
cruise (mGal) Vgs: The shipboard gravity at the start of the cruise (mGal) Vg: The shipboard gravity at the measurement
time (mGal) D: Drift value (mGal/day) Ts: The start time of the cruise (day) T: The measurement time (day)
E: Eoetvoes correction (mGal) H: Height from sea surface of the shipboard sensor position (m) β: Free-air gradient
0.3086 (mGal/m)